Melt-spinning process



Jan. 2, 1968 1.. CENZATO MELT- SPINNING PROCESS Filed May 4, 1966 J LORENZO csnz ro United States Patent 3,361,859 MELT-SPINNING PROCESS Lorenzo Cenzato, Bologna, Italy, assignor to E. I. du Pont de Nemours and Company, Wilmington, Del., 2 corporation of Delaware Filed May 4, 1966, Ser. No. 554,620 7 Claims. (Cl. 264-176) ABSTRACT OF THE DISCLOSURE An improvement is disclosed in the process of extruding synthetic organic polymer through spinneret orifices, cooling the extruded polymer in a gaseous medium to form filaments and thereafter drawing the filaments at least 2.8x to a tenacity of at least 4 grams per denier. Improvements are shown to result from a controlled retarded cooling of the extruded polymer. The gaseous medium is heated to have temperatures adjacent to the filaments which decrease with distance from the spinneret in a manner defined by temperature-time formulas.

Cross-reference to related applications This is a continuation-in-part of application Ser. No. 256,083, filed Feb. 4, 1963, as a continuation-in-part of application Ser. No. 25,576, filed April 29, 1960, both now abandoned.

This invention is concerned with the preparation of filaments from high melting, highly viscous polymers by melt spinning, cooling to solidify the filaments and then drawing the filaments.

It has been found that the spinning process itself limits the properties of the drawn filaments. Prior to the present invention, attempts to use higher molecular weight polymer at conventional spinning speeds have not produced uniform and improved filaments. Furthermore, attempts to increase the productivity of spinning processes by raising the spinning speed have resulted in a lowering of physical properties. These attempts have caused an increase in the orientation introduced in the spinning process, which reduces the maximum obtainable draw ratio and filament tenacity, as discussed in column 3 of Paulsen US. Patent No. 2,918,346, dated Dec. 22, 1959. Although there are many variables that affect the amount of orientation introduced, the melt viscosity of the polymer and the spinning speed are the primary variables in commercial-scale production of filaments which are from about 6 to 200 denier per filament as spun (i.e., before drawing).

As a general guide it has been found that the problem of spinning orientation becomes significant when the product of the melt viscosity (1; melt) of the fiber in poises times the spinning speed (V) in yards per minute (y.p.m.) is at least 7.1)(10 poises-y.p.m., and the problem is extremely serious when this product is greater than 15x10 poises-y.p.m.; where 1; melt is measured at a temperature of 30 C. above the crystalline melting point (T and at a shear rate at or about seconds and V is the velocity of the spun fibers after they have solidified by cooling and before they have been drawn.

The following tabulation of melt viscosities and commonly used molecular weight-dependent properties of some polymers will serve as background for this invention:

The present invention is an improvement in the process of extruding synthetic organic polymer through spinneret orifices at atemperature (T at least 20 C. above the melting point (T of the polymer, cooling the extruded polymer in a gaseous medium to form filaments, and thereafter drawing the filaments at least 2.8x to a tenacity of at least 4 grams per denier (g.p.d.). The improvement is in providing a controlled retarded cooling of the filaments by heating the gaseous medium to have gas temperatures (T adjacent to the filaments which are less than T +100 C. near to the spinneret, are less than along the filaments, and are greater than Ts35-18t 6200 n melt 17 melt 6200 The improvement is particularly applicable to the meltspinning of polymers such as polyethylene terephthalate under conditions such that 1; melt times the spinning speed (V) in yards per minute is greater than 15 10 poisesy.p.rn. The process is particularly useful in the preparation of fibers of high viscosity polymer for industrial purposes where tenacities of 8 g.p.d. or more are needed. For example, a high viscosity polyester (1 melt of 6200 or more) is preferably extruded at temperatures of 320 C. or more into hot gas having a temperature of at least 320 C. near the spinneret, the extruded fiber is solidi- T ++50 log r3 fied under the retarded cooling conditions specified, and the cooled fibers are drawn at least 6X. Preferably the gas temperatures (T are less than T mi I 6200 s n 7 melt and preferably the maximum temperature of the hot gas (T is at least T 20 C. adjacent to the spinneret.

Typical values of the maximum spinning temperature, as calculated from the formula T =T +75+50 log (1 melt/ 6200), follow:

Polymer Poises Maximum m C.) 1 melt '1; C.)

from which the following typical values may be calculated:

1; melt V tm in.

Preferably the temperature of the gas (T should be controlled critically until it reaches a value of (T -60) after which it can cool very quickly. This is equivalent to a T T value of about 120 C. for the examples of polyesters given subsequently.

Normally AT will occur adjacent to the spinneret. However, it may be delayed for as much as 0.12 to 0.15 seconds with some types of heating and particularly with negative AT values, as when T increases from an initial value to a maximum and is then cooled.

The process of this invention is particularly valuable in processes where spinning orifices of 6 to 30 mils in diameter are used with spin stretch ratios [(Orifice DiameterV/(as-spun fiber diameter) of up to 100 to produce as-sp-un fibers of 6 to 200 d.p.f. for drawing at draw ratios of 3.5 or more.

It may be desirable to extrude the molten polymer into an atmosphere of inert gas, i.e., a gas substantially free of oxygen. Suitable inert gases are hot nitrogen and carbon dioxide, as well as inert organic vapors. The use of an oxygen-free gas immediately below the spinneret reduces degradation encountered at that point when polymers, such as poly(ethylene terephthalate) having a relative viscosity (RV) above about 50 or 55, are extruded into air. The use of an oxygen-free gas can reduce the normally encountered relative viscosity loss by as much as 5 to 6 units, while at the same time reducing the normally encountered gain in carboxyl group content by as much as 6 to 8 eq./10 g. The improvement obtained with an inert gas is even more pronounced when higher RV polymers are used, i.e., 75-100.

It is considered that it is the melt viscosity in the extruded polymer and in the semi-molten filament that controls the effects of this process. If an extremely high molecular weight polymer having a relative viscosity of 60 to 100, for example, is mixed with a plasticizer, its viscosity at the extrusion temperature will be lowered. Such a polymer, for purposes of this invention, should be considered as having an effective molecular weight equal to a pure polymer having the same melt viscosity at the given temperature. For example, a poly(ethylene terephthalate) of RV 70 containing 2% by Weight of diphenoxyethane has a melt viscosity of 19,000 poises at 310 C. and at a shear rate less than 10 reciprocal seconds. The pure, unplasticized sample of the same polymer of RV 64 has the same melt viscosity under these same conditions. The palsticized polymer should be considered as having an RV of 64 for this invention.

This process is characterized by a substantially lower spinning tension than is normally found. With poly(ethylene terephthalate) the threadline tension, measured at a point where the filament temperature is less than the second-order transition temperature (about C.) should not exceed the following values:

Threadline tension Polymer RV (grams/denier) Maximum Preferred Both the spinning speed and the threadline tension refer to measurements made after the filaments have cooled below the second-order transition temperature and before being subjected to increased tension in any subsequent drawing operation which may be coupled with the spinning process. The spinning speed is preferably less than 1300 yards per minute and, in a coupled spinning and drawing process, should preferably be about 200 to 500 yards .per minute (the wind-up speed after drawing in a coupled process is muchhigher, of course).

The products made :by the improved process of the present invention are characterized by an improved uniformity of structure within the shaped articles and between simultaneously extruded articles. The products made by extrusion alone are noted for their lower levels of birefringence and lack of orientation when compared to products made at the same speeds using conventional processes. Whereas commercially available polyester fibers show a pronounced index of refraction gradient (as determined with an interference microscope) across the filament cross section, fibers made by the present invention have a greatly reduced gradient across the fiber crosssection.

The oriented filaments of this invention also show an improved intrafilament uniformity over known products. The improvement in polyester filaments is especially pronounced, as illustrated in the drawings wherein FIGURE 1 is an electron micrograph (26,000Xmagnification) of a typical filament of this invention; and

FIGURE 2 is a corresponding micrograph of a filament which is typical of the prior art.

Polyester filaments of the prior art contain a skin of about /2 micron thick that can be peeled from the fiber. This skin shows the first arc. (003 Miller Index) on the axis corresponding to the fiber axis in an electron diffraction pattern to be indistinct and single. A diffraction pattern of the whole fiber shows the same are as sharp and split into two maxima. Boththe peeling and the whole fiber of products of this invention show the first are on the axis as sharp and split into two maxima, thus showing the uniformity. of the new product.

The oriented products of this invention also display a very high level of crystallinity in conjunction with excellent physical properties such as lack of brittleness, high 140 C. flex resistance, high tenacity and excellent resistance to fibrillation which has not been previously attained. Polyethylene terephthalate fibers with a denier per filament greater than 2.5 and having a flex life of considerably more than 200,000 cycles at 140 C. are obtained.

The improved interfilament uniformity of the oriented filaments of this invention is shown by such properties as a ratio of yarn to average single filament tenacity of 0.9 or greater and by the substantially straight and sharp stress-strain curves obtained on yarn.

Although improved results are obtained in accordance with the present invention with all synthetic fiber-forming organic polymers under the previously-defined conditions, it is particularly useful with the types of polymers illustrated in the examples. There is an optimum set of conditions for each particular polymer at a given spinning speed which offers the most satisfactory results in the process of this invention. In general, these conditions will correspond to the maximum draw ratio (or minimum birefringence) obtained when spinning the filaments at various gas temperature profiles at a given speed, and are readily determined by experiment within the defined limits. After the filaments have been cooled under properly controlled temperature conditions to a temperature of about 100 C. the filaments can be cooled very lowly or very rapidly. The use of secondary quenching means such as liquids, mists, cold gases, etc., Will be apparent to one skilled in the art.

The invention provides improved results with polypropylene, and the new higher melting, higher density forms of polypropylene having a decreased amount of chain branching and/or isotactic structures are particularly suitable in this process. Because of their commercial availability, ease of processing and excellent properties, the condensation polymers and copolymers, e.g., polyamides and polyesters, and particularly those that can be readily melt polymerized to high viscosity, are preferred for application in this method. Suitable polymers include fiber-forrning polyamides and polyesters of types described, e.g., in U.S. Patents Nos. 2,071,250, 2,071,253, 2,130,523, 2,130,948, 2,190,770, 2,465,319, 2,916,574 and 3,051,212; and in Belgium Patent 668,703 granted February 24, 1966, and British Patent 604,073 dated June 28, 1948.

Particularly suitable polyamides include polyhexamethylene adiparnide and polyamides of alkanedioic acids with diaminohydrocarbons [preferably bis (para-aminocyclohexyl)methane], where the hydrocarbon portion is a divalent, saturated, cycloaliphatic group.

The preferred polyesters to be used in this invention are obtained from terephthalic acid wherein at least 75% of the recurring structural units of the polyester are glycol terephthalate structural units. These should be fiberfonning and have a relative viscosity of at least about 25. Such polymers may be represented in a more general way by the formula HOG(OOCA-COOG),YOH where G and A- are divalent organic radicals corresponding, respectively, to the radical in the initial glycol, G(OH) and to the initial dicarboxylic acid, A(COOH) and y is a number sufiicient that the polymer is of fiber-forming molecular weight; at least about 75% of the A- radicals being terephthalate radicals. The terephthalate radical may be the sole dicarboxylate constituent of the recurring structural units, or up to about 25% of the recurring structural units may contain other dicarboxylic radicals, such as the adipate, sebacate, isophthalate, S-(sodium sulfo)-isophthalate, bibenzoate, hexahydroterephthalate, diphenoxyethane-4,4'-dicarboxylate, or p,p'-sulfonylbibenzoate radicals, derived from the corresponding dicarboxylic acids or ester-forming derivatives thereof. The glycol may be trimethylene glycol, tetramethylene glycol, hexamethylene glycol, decamethylene glycol, 2,2-dimethylpropanediol, trans-p-hexahydroxylylene glycol, diethylene glycol, bis-p-(fi-hydroxyethoxy) benzene, bis-1,4-(l3-hydroxyethoxy) -2,5-dichlorobenzene, or his [p (,8 hydroxyethoxy)phenyl]difiuoromethane. Those may be used alone or in mixtures, e.g., ethylene glycol plus up to about 25 mol percent of the abovementioned glycols.

Test procedures The flex life (flex resistance) of a filament is determined by clamping one end of a filament of at least one inch length to a frame rotating in the plane of the vertical with the filament being weighted by an amount of 0.6 gram per denier (g.p.d.) and having a smooth wire 3 mils in diameter positioned horizontally at the midpoint of the filament. Twenty-one specimens are simultaneously bent repeatedly through over the Wire while under tension. The number of cycles required to cause failure of 11 filaments is accepted as the test result.

In the examples, the relative viscosity (RV) is the viscosity of a solution of polymer relative to that of the solvent and is a measure or" the molecular weight. The polyamide solutions contain 5.5 g. of polymer in 50 ml. of formic acid or of formic acid/phenol (50/50 by weight), and the viscosity is measured at 25 C. The polyester solutions contain 2.15 parts of the polymer in 19.35 parts by weight of a 7/10 mixture of 2,4,6-trichlorophenol/phenol and the viscosity is measured at 25 C.

Gas temperatures (T should be measured with an aspirating thermocouple placed as close as possible to the filaments without disrupting the spinning. The hot gas is drawn in over a thermocouple that is shielded from radiation of the equipment.

The maximum draw ratio of a fiber is determined by drawing (or stretching) a fiber around a metal pin, over a plate, or through a bath at a given temperature by means of a feed and a delivery roll having continuously variable speeds to the maximum amount possible without breaking the fibers. Draw ratio is defined as the ratio of the surface speeds of the delivery roll to the feed roll or the ratio of the drawn length to the as-spun length of the fiber. Unless otherwise noted, all physical properties are determined on fibers drawn to the maximum draw ratio.

All birefringence measurements are made on as-spun (undrawn fibers) by examining a single fiber under crossed nicol prisms in a microscope using a calibrated quartz compensating wedge (Textile Research Journal, August, 1952).

Example I Poly(ethylene terephthalate) of relative viscosity 40.5 (crystalline melting point of 265 C.) and containing 0.15% TiO is extruded from a melt at 288" C. through a spinneret containing 20 holes of 16 mils in diameter located on a 2%" diameter circle at 285 C. and the filament (23 d.p.f.) wound up at 500 y.p.m. Cooling of the filaments is retarded under controlled temperature conditions with a muffle furnace (7" high), comprising exposed electrical resistance wires coiled on the inner surface of a ceramic cylinder affording an open passageway of about 3" in diameter, centered below the spinneret. The apparatus may be arranged as disclosed in Hardy U.S. Patent No. 2,296,202, except that the means for electric heating must be suitable for providing a closelycontrolled temperature gradient. After the threadline is strung up through the furnace, two thermocouples are carefully inserted between two adjacent filaments at the uper and lower edge of the furnace so that they measure the temperature of the air between each pair of filaments. In addition, a third thermocouple is located half Way up the muflle furnace approximately of an inch towards the threadline from the heating element. When the thermocouples are in position, the unit is carefully raised toward the spinneret until the top of the mufile furnace is sealed against the bottom of the spinning machine head. This effectively seals the filaments from any stray currents of air between the spinneret and the muffle furnace.

Samples of yarn are collected under difierent conditions of heating in the muflie furnace and drawn over a -inch long plate heated to 185 C. located between a 3-inch diameter preheating roll at 90 C. (4 wraps) and a cold drawing roll. The results are given below in Table 1. Item 01 represents the values on filaments spun from the same polymer at the same speed and spinneret temperature but using conventional cross flow cooling as disclosed in US. Patent No. 2,273,105. The improvement in properties of the filaments spun under the process of this invention (items a, b and c) as compared with the use of a conventional process (d) is apparent from the data. The temperatures indicated for items a, b and 0 fall within the previously defined limits of AT.

1 N0 heater.

A similar improvement in comparison with conventionally processed yarn is obtained when the polyester, poly(trans-p-hexahydroxylene terephthalate) of relative viscosity 39, and the copolyester, poly[ethyleneterephthalate/S-(sodium-sulfo)isophthalate] 98/2 mol percent ratio, of relative viscosity 18.5, are separately spun under conditions within the above limits.

Example II This example shows additional unexpected properties of the polyester filaments of this invention.

(A) Following the procedure of Example I, poly(ethylene terephthalate) of 40.5 relative viscosity is extruded through a mufile furnace at condition falling within the limits for AT as previously defined, the yarn being wound up at 1000 y.p.m. Individual filament have a tenacity of 9.3 g.p.d. after maximum drawing of the spun yarn under the conditions of Example I. The yarn tenacity, 9.0 g.p.d., (97% of filament tenacity) is unexpectedly high compared to conventional products and is considered to reflect the unusual uniformity of such products and corresponding absence of weak filaments.

(B) A control yarn is prepared from poly(ethylene terephthalate) of 45 relative viscosity, i.e., of higher molecular weight than the above polymer. The yarn is prepared under the best possible conventional quench spinping conditions, using a cross-flow quench and advancing the solidified filaments at 150 y.p.m. to a drawing step as above for maximum drawability. Despite the higher molecular weight of the polymer used (when processed in accordance with the present invention, higher molecular weight polymer normally provides improved tenacity and flex resistance), the single filaments have a tenacity of only 7.5 g.p.d. and the yarn has a tenacity of only 6.5 g.p.d. (86% of filament value).

Product A has a significantly higher degree of crystallinity than the control (a crystallinity index number of 39 vs. 36 for the control-ASTM International Symposium, October, 1958, by W. Stratton).

The actual level of crystallinity depends upon the heat treatment of the fiber or film. It has been observed that under the same heating conditions the products of this invention give a higher level of crystallinity than products spun under conventional methods.

The flex life of product A is 560,000 cycles compared to 86,000 cycles for the control when tested as described previously at 140 C. The tenacity of the filaments not broken by the flexing is 8.9 g.p.d. as contrasted with 4.8 g.p.d. for the control. Photomicrographs of the ends of the filaments broken in the test show filaments A to have a clean break'with no signs of fibrillation (i.e., splitting Whereas the control ends are completely frayed and fibrillated.

Samples of product A and the control are split longitudinally, soaked in n-propylamine for one hour to etch the amorphous regions, Washed with fresh amine and dried. Metallic chromium is vacuum deposited on the filaments, and the organic material dissolved in trifiuoracetic acid. Electron micrographs (26,000 times magnification) of the replicas of product A and the control are shown in FIGURES 1 and 2 respectively. In each figure the upper dark portions represent the surface of the fiber, the light central area represents a skin of about 1.5 micron in thickness and the darker area at the bottom represents one-half of the core of the filament. The transversal structural uniformity of fiber A is apparent in FIGURE 1. The skin and core can scarcely be distinguished, both exhibiting high crystallinity and orientation. On the other hand, the skin of the control (FIG. 2) exhibits low crystallinity and orientation, and is markedly different from the core.

A second control yarn is prepared of the same polymer but spun at 600 y.p.m. under optimum quench-spinning conditions. It has a maximum filament tenacity of 5.9 g.p.d., a maximum yarn tenacity of 5.1 g.p.d. (87% of filament tenacity) and a flex life of les than 100,000 cycles at 140 C.

Example Ill Yarns are prepared according to the conditions of items (b) and (d) (control) in Example I, but drawn 5.2 and 4.7 times (maximum possible) over a C. hot pin. The physical properties of the drawn yarn are shown below:

TABLE 2 Item Control Spinning speed (y.p.m.) 750 600 Filament tenacity (g p d 8.1 5. 1 Elongation at b1 eak (percent). 15 12. 5 Yarn tenacity (g.p.d. 7.9 4.4 Flex life, room temperature 800, 000 800,000 Flex life, C 1, 020, 000 200, 000 Tenacity of unbroken filaments after 11 g at 140 C. (g.p.d.) 7.9 3.6

The heater used in this example comprises two concentric aluminum tubes 11 inches long. The inner tube through which the filaments pass has an inside diameter of 8 inches. Resistance heaters are located in the annulus between the 2 tubes and are controlled by a thermocouple adjacent to the wall of the central passage and located about 2 inches below the top. The heater annulus has a metal bottom which, along with the outside face of the heater, is well insulated. The heater is mounted to the spinning head through a 1-inch layer of hard insulating material so that the heater and insulation provides a chamber, open to air only at the bottom that extends 12 inches down from the face of the spinneret.

Molten poly(ethylene terephthalate) is extruded through a spinneret having 192 holes of 0.3 mm. diameter. The extruded filaments pass through the heater and are then gently quenched by a conventional cross-flow of air from one side of the threadline, Birefringence is determined on samples of the asspun (undrawn) filaments.

Values of the spinning variables used are given in Table ditions.

As spun Maximum Birefringence Maximum Yarn Tanae- Item (X10 Draw Ratio ity (g.p.d.)

20 5. 4 8. 1 14 6. 8. 9 4 ll 6. 5 9. 4 No heater 52 3. 5 5. 1

Item 5 shows the effect of a low spinning velocity (200 y.p.m.) as compared to item 4 at 350 y.p.m. using the same heater control temperature and having the same maximum T Items 6 and 3 can also be compared for different speeds at the same heater temperature and similar maximum T values. The necessity for cooling the fibers more slowly at the higher speed is apparent from the birefringence values in Table 3.

Item 7 is prepared as above but with the addition of a 4 inch insulated tube to the bottom of the heater. This decreases the rate of cooling over that afi'orded by the heater alone. When the spin is repeated with all conditions the same, except that the heater and extension are removed, filaments having a birefringence of about 0.0051 are obtained.

The heater has a plain metal tube with a cross-section of a frustrum of a cone that extends about 16 inches below the bottom of the heater. The outer surface of the heater proper and the extension are well insulated. The total distance below the spinneret in which the cooling rate is controlled is 24 inches.

Molten poly(ethylene terephthalate) is extruded from a pool at 310 C. through the spinneret of Example IV. The extruded filaments pass directly through the heater. Inert gas at the rate of about 7 cubic feet per minute C.) is heated to about 380 C. in a preheater and there passed to the heater. The resistance heaters are adjusted to give a gas temperature adjacent the spinneret of about 320 C. The temperature profile within the heater is given in Table 3, item 8. Upon leaving the heater extension the filaments pass through a 4-inch air space and then through a radial quenching device which directs a stream of room-temperature air at a velocity just short of that causing turbulence in the threadline. The threadline then passes over a finish roll where a lubricating finish is applied, and then around an unheated feed roll operating at a speed of about 500 yards per minute. Samples of yarn taken at this point have a birefringence of 0.0007 and a relative viscosity of 50.

From the feed roll the threadline next passes through a steam jet where steam at a temperature of 350 C. is impinged on the threadline to heat the yarn and establish a draw point. From the steam jet the yarn passes to and around a cold draw roll operating at a speed sufficient to give a draw ratio of 6.0. The threadline then passes to a conventional windup. The drawn yarn has a tenacity of 9.2 g.p.d. and a break elongation of 13%.

Example VI This example shows the more stringent conditions required to process higher molecular weight polyesters.

TABLE 3 Spinning Denier Bire- Item RV Speed per Fil- T, d t '1; AT fringenee (y.p.m.) ament 0.) (inches) (sec. 100) C.) $221118 Example V Molten poly (ethylene terephthalate) 1s extruded, from a 315 C. melt at 5900 psi. through a spinneret containing 192 holes of 20 mil diameter at a rate of 35 pounds per hour, at 331 C. (calculated) into a zone of heated gas in a heater, through a tubular extension into ambient air, and then through a radial quenching device to a finish roll and a feed roll running at 246 y.p.m. where samples of the as-spun yarn are taken. The yarn continues onward of inert gas that passes into the plenum and out the screen. 75 through a drawing zone.

The heater is 6 inches long and consists of 3 concentric metal tubes, top and bottom walls. The innermost tube of 9.2-inch inside diameter extends from the bottom wall to about 1 inch from the top, the middle tube extends from the top wall to about l inch from the bottom. The outer tube contains electrical heaters on its inner wall and is insulated on the outside. Preheated gas at a rate of 4.6 s.c.f.m. (i.e., cubic feet per minute calculated for standard conditions of C. and 1 at-m.) enters the outermost plenum, is distributed by the baflles and enters the innermost space. Both plenum chambers containa thermocouple and the heaters are adjusted so that both thermocouples are at the same temperature. The heater is separated from the spinning block by a 2-inch long insulator tube. A 30-inch long insulated metal tube of 9.2-inch inside diameter is attached below the heater.

Temperatures are given in Table 4 with the as-spun birefringence values and draw ratios. Items (b) to (d) have an as-spun denier of 52 d.p.f., a spin-stretch ratio of about 42 and a yarn relative viscosity of -65. The control item (a), spun from a difierent polymer batch and 12 a spinneret having 101 holes of 15 mil diameter at a rate of 18 pounds per hour with a hot gas flow rate to the heater of 9.2 s.c.f.m. The times (t) in seconds X 100 from the spinneret to the distances (d) given have been calculated for a yarn speed of 385 y.p.m. Alli-tems have tenacities of at least 8.5 g.p.d. at elongations of about 13 to 14%.

The excessive reduction of relative viscosity in item (b) is apparent.

Items (c) and (d) are extruded through a spinneret having 192 holes of 20 mil diameter at a rate of pounds/hour with a gas flow rate to the heater or 13.8 s.c.f.m. The Denier C is the ratio, 100 a/average diameter, where a is the standard deviation of the diameters of different filaments in the yarn and represents the uniformity of the yarn.

The percent Uster value is a measure of the uniformity V of denier along the length of a yarn.

Item ((1) which uses gas temperatures greater than the limits of this invention is significantly less uniform than item (c).

TABLE 5 Gas T(e n(1)p;erature Relative Viscosity Item d AT 1: Denier Percent (inches) (sec. 100) CV Uster In At 11 Feed Yarn plenum with the heater extension removed, has an as-spun denier of 37 and a yarn relative viscosity of 59.

TABLE 4 Gas Temperature C C.) Bire- Machine Item (1 AT t fringence Draw (inches) (see.X) value Ratio In At (1 X10 plenum 1 Not drawable.

Example VII This example shows the effects of excessive heating of filaments.

Molten poly(ethylene terephtha'late) is extruded, from a 300 C. melt at a pressure averaging about 6200 p.s.i. through a spinneret, at 317 C. (calculated) into a heater similar to that of Example VI but having a 16"-long insulated metal extension tube, over a finish roll and a feed roll running at 385 to 387 y.p.m. The yarn is then quenched and drawn in a steam jet.

Results are given in Table 5. The gas temperatures given have been calculated, using the temperature of the block, the polymer throughout, the hot gas temperature Example VIII is approximately the same as the poly(hexamethyland flow rate. Items (a) and (b) are extruded through ene)adipamide component or about 2700 and 4100 poises 13 at 295 C. (T +30 C.) for shear rates of up to 10 secondsfor 70 RV and 80 RV, respectively.

The polymer is extruded from a pool at 282 C. through a spinneret containing 140 orifices of 12 mil diameter.

elongation. The significantly higher tenacities of items (is) and (d), as compared with items (a) and (c), are apparent. It is believed that the lower average birefringence values and the more uniform birefringence values obtained The polymer melt has a pressure drop between the melt will give even greater improvements in tenacity under betpool before the pump and the orifices of about 6100 tcr drawing conditions. and 7000 p.s.i. respectively, for the 70 and 80 RV poly- The spin-stretch value (orifice diameter) (as-spun mers. The temperature of the extruded polymers is calfiber diameter) for items (b) and (d) is about 21.

TABLE 6 Birefringence RV Spinning T, (1 T 1; valneXlO Drawn Item yarn Speed 0.) (inches) 0.) AT (sec. Ten./E (y.p.m.) (g.p.d.)

X IT (percent) a so 447 301 1 239 62 0.37 7.9 1.3 8. 5/154 9. 74 249 52 3.8 11.75 215 86 4.6 13.75 175 126 5.4 c 70 439 299 6.9 0.9 8.9/l5.8 d- 70 424 299 3. 75 253 36 1. 5 3. 5 0. 4 9. 3/15. 3

culated to be 299 and 301 for the 2 polymers. The ex- Example IX Lruded filaments pass through a 2.75-inch long recess in the spinning block, through the controlled heating zone, A polyarmde P p from (p y through a conventional chimney for rapid cooling of the heXyDmeihahe (Containing 90% 05 trails-(Tells configurafilaments, over a ceramic guide, a conventional finish roll, iiehs) and dedeeahedieie acid is used- The P y flake and to a feed roll (3 wraps) where samples of the as-spun has afeiaiive Viscosity 0f 7 as measured in 98% filaments are taken for birefringence determinations. The formic acid/Phenol, 50150 y Weight at and has a filament bundle is passed from the feed roll to a two'stage crystalline melting Point Of drawing process consisting of 2 snubbing pins at 80 C., The p y is extruded from a melt at at a first draw roll (for 3.5x draw), a hot tube at 200 C. about 7000 P- Pressure through a Spinneret (containing (1.5 wraps) along about 28 inches of its length, a second 5 orifices 0i 9 mil diameter) into a Zone heated y steam, draw roll, a hot roll at 215 and a relaxing roll to permit ihehee through a quenching Zone Provided y ambient 6% shrinkage between the hot roll and windup. The to a finish foil and to a feed I011 at 115 Y-P- Where second d 11 Speed i k constant at 2500 p m samples are taken for birefringence measurements. The for each spin, with the other rolls and wheels being Y is Passed from the feed fell to a two-siege drawing adjusted to give difierent spinning speeds and draw ratios. Process consisting of a 0-75"iI1eh diameter metal P at The spinning pumps are adjusted to give a drawn and for a 3X draw: Over a metal Plate inches relaxed total denier of 840 for each run. long) ai to a first siege draw T011, thence along The controlled heating zone is provided by a radial the Outer surface of iiihe p heated at to gas diff f 4 125-i length and 974 inside 235 C. to the second state draw roll and then to a windup. ameter consisting of an inner screen, a plenum chamber The total draw ratio is Varied from X to X to g and an entrance for preheated gas (essentially N and the desired elongationco t a t equivalent to 3 bi f t/ i t at 0 The heated zone consists of (1) a 0.5-inch resess in the C. and 1 atmosphere. An 8-inch long metal tube of conical spinning block all insulated metal tube 0f conical shape is attached to the bottom f th diff Th b tion with an inside diameter of 4 inches at the block and is shaped at a 30 angle to the vertical and is truncated an inside diameter of 6 inches at the bottom, a radial from 8 inches vertical distance in the back to 4.25 inches steam diihlsei" consisting of a e-iiieh inside diameter meiai vertical distance in the front. Since the spinning block, Screen 6i11ches10ng, a concentric plenum chamber, a difiuser and tube are tightly sealed, the T temperatur tribution wall and an outer concentric chamber containing of the gas for the first 3.75 inches must vary between eieeiiieai heating eiemehis and an entrance for p the temperature of the spinning block (290 C.) and the heated steam, a metal Cone of 3-i11eh altitude With a fi t measured temperature base diameter of 6 inches, and (5) a metal tube of 3-inch The temperature of the gas (T adj t t th inside diameter connected to the apex of the cone and exthreadline is measured by an aspirating thennccouple tending 28 lIlChfJS from it. Saturated steam at about 100 while spinning. Only the inflection points of the T vs. is supplied to the suPeIheaier at a Tate suiiieiehi to give distance (d) curve are given inTable 6. The temperatures p of steam from the lower end of the assembly of the gas in the plenum chambers for items (b) and (d) yp y about 4 'r cubic feet P minute are 300 and 315 C., respectively. culated for standard conditions of 0 C. and 1 atmosphere F comparative purposes i i i d i h h pressure). The heat to the superheater and the heaters in gas difiuser and the conical extension removed, and with the Piehum are adjusted to give the desired temperatures cross flow quench from the bottom of the block. Typical in the P All units are Connected together and the lt are t d i T bl 5 as it d entire assembly connected directly to the block of the spin- From the results given in Table 6 it is seen that the Ring Positioncontrolled cooling of this invention (items (in) and (d)) The temperature of the steam adjacent the iiielheiiis is produces 315- pun yam with lower ave agg birefringence measured With an aspirating thermocouple at l-inch intervalues (X) and with lower standard deviation (0') than is Vais along the length of the ihreadiifie under difiefent e011- obtained ith ti l cross fl quenching (i 7 ditions. Values at inflection points on a T vs. distance (a) and (0)). The birefringence values do not vary signi- P are giwih in Table The temperature of the ficantly over the range of spinning speeds used of from extruded P y s) is estimated to h shout 424 t 455 y p m based on the block temperature of 333 C. and the pres- Sarnples are selected at a given spinning speed, and sure p of 5000 P- hence a given draw ratio, to have approximately the same Item (e) is a control spun under the same conditions 15 but with all the tubes and heating devices removed from the block and replaced with a conventional crossfiow quenching chimney.

The as-spun fiber has a denier per filament of about 36 d.p.f. The spin-stretch ratio is thus about 11.

The yarns for all items have an RV of 138, which polymer has a melt viscosity of about 25,000 poises at 330 C. and at a shear rate of up to 0.1 second The great reduction in birefringence of the as-spun yarns of items (a) to (d) over the control item (e) is apparent. The control yarn (item e) is drawn to give a tenacity of 5.4 g.p.d. at 11.7% elongation. The yarn tenacities of items (a) to (d) range from 6.4 to 7.0 g.p.d.

at 10.6 to 11.1% elongation.

15 wheel where samples are collected. A spinning temperature (T of about 243 C. is estimated.

The heated zone is provided by a l2-inch long 4-inch inside diameter, metal tube which has electrical heaters on its exterior, and is well insulated, and is held in place beneath and close to the spinneret.

Filaments are spun under 2 heating conditions, (B) and (C), (with medium and high heater control settings, respectively), and under one control condition (A) with the hot tube removed and replaced by the radial air quench. Temperature profiles of the conditions (in C.) are given below. The time (t in seconds 100) to reach 11 inches is 12.1, 6.0 and 4.0 for 150, 3 and 455 y.p.m., respectively.

TABLE 7 Temperature C C.) Bire- Drawn Item d AT 1; fringence Ten/E (inches) (see. l00) value (g.p.d.) Plenum T, at d X104 (percent) a 360 352 1 1. 4 42 6. 6/10. 6 368 6 21 8.6 333 s 36 11. 5 375 28 14.3 300 12 +47 17.3 255 14 +92 204 20 143 29 b 327 347 1 0 66 6. 4/10. 6 336 2 11 2.9 338 8 9 11.5 322 10 14.3 228 14 119 20 192 20 155 29 e 306 330 1 17 1. 4 so 7. 0/11. 0 310 3 37 4.3 303 s 39 11.5 296 10 51 14.3 206 14 141 20 154 20 193 29 e 205 5.4/11.7

1 Heater not used.

Example X Commerc1a1 1sotact1c polypropylene of the following Gas Temperature Pwfile propert1es is used: Distance (inches) A B 0 Melt Index at Melt Flow Rate Viscosity Polymer 190 C./2,160 g. 230 C./2,160 g. (poiscs) AT AT AT at 200 C.

Samples are produced at spinning speeds of 150, 300 and 455 y.p.rn. with different gas' temperature profiles for the three polymers, typical denie'rs for the three speeds being, respectively, 39, 20 and 15 d.p.f. The spin-draw ratios (D /D thus have a maximum value of 70. From the results given in Table 8 it is seen that use of the controlled cooling of this invention (items 11, e and TABLE 8 As-Spun yarn properties It T Gas P l Blr Irl X10 em em er- 0 er e ngence atu e ym Melt Melt Profile Index Viscosity Spun at Spun at Spun at (parses) y.p.m. 300 y.p.m. 455 y.p.m.

a A II 9. 3 l3. 7 15. 3 4. 9 14, 500 b B H 3.0 6.1 10.0 5.8 12,000 c C II 1. 3 3. 6 5. 7 7. 0 10, 000 d A III 12. 4 16. 1 17. 6 2. 0 20,000 6 B III 4.9 8.5 11.3 2.7 f A I 7.2 11.3 13.3 9.5 7,500 g B I 2. 0 4. 6 7. 5 10. 9 6, 000

1 Estimated.

g) gives a significant decrease in the birefringence at all speeds and with all 3 polymers. Item (c) represents excessive heating, since the filaments have degraded significantly.

Since many different embodiments of the invention may be made without departing from the spirit and scope thereof, it is to be understood that the invention is not limited by the specific illustrations except to the extent defined in the following claims.

1. In the process of extruding synthetic organic polymer through spinneret orifices, at a temperature (T at least 20 C. above the melting point (T of the polymer, into a gaseous medium and cooling the polymer to form filaments and drawing the filaments at least 2.8x to a tenacity of at least 4 grams per denier; the improvement of providing a controlled retarded cooling of the fi1a ments by heating the gaseous medium to have gas tem peratures (T adjacent to the filaments which are less than T +100 C. near to the spinneret, are less than along the filaments and are greater than 7 melt until T =T 150 C., where AT is equal to T minus the maximum T t is 100 times the elapsed coding time in seconds, and r is the viscosity in poises of the extruded filaments at a temperature of T +30 C. measured at a shear rate of up to 10 seconds- 2. The process as defined in claim 1 wherein the product of the melt viscosity (1 times the spinning speed (V) in yards per minute is at least 7.1 X 10 poises-y.p.m.

3. The process as defined in claim 1 wherein the product of the melt viscosity times the spinning speed is greater than 10 poises-y.p.m.

4. The process as defined in claim 1 wherein the extrusion temperature (T is less than elt T ++50 log 0 8 5. The process as defined in claim 1 wherein a gas temperature (T of T l50 C. is reached in a time, in x seconds, at least as long as Where V is the spinning speed in yards per minute.

6. The process as defined in claim 1 wherein the synthetic organic polymer is a high molecular weight polyrner having a melt viscosity (7 of at least 5000 poises selected from the class consisting of polyesters, polyamides and polypropylene.

7. The process as defined in claim 3 wherein the synthetic organic polymer is an ethylene terephthalate polyester having a melt viscosity (7 of at least 6200 poises.

References Cited ALEXANDER H. BRODMERKEL, Primary Examiner. J. WOO, Assistant Examiner. 

